Tick-borne bacterial pathogens of humans cause significant morbidity and mortality throughout the United States and abroad. Lyme disease, caused by Borrelia burgdorferi, is the most prevalent arthropod-borne disease of humans in the United States and many other countries throughout Europe and Asia. Tick-borne relapsing fever, caused by Borrelia hermsii, is endemic in scattered foci throughout many regions of higher elevation in the western United States. Our work has focused on two areas: 1) to improve on the serodiagnosis of Lyme disease and relapsing fever by using recombinant DNA technology to clone genes of spirochetes that express proteins that induce specific and detectable antibody responses; 2) to examine how spirochetes adapt to their tick and mammalian hosts. This work requires that we maintain colonies of Ixodes scapularis and Ornithodoros hermsi, respective tick vectors of Lyme disease and relapsing fever spirochetes, and infect these ticks via a laboratory mouse - tick cycle. Efforts toward improving serodiagnosis during the past year have been directed at cloning and expressing the glpQ gene, encoding glycerophosphoryldiester phosphodiesterase, of Borrelia recurrentis, the causative agent of louse-borne relapsing fever. Previously we showed that GlpQ of Borrelia hermsii is an immunogenic protein with utility as a serological test antigen for discriminating tick-borne relapsing fever from Lyme disease. This past year, we cloned and expressed the glpQ gene from B. recurrentis and used recombinant GlpQ in serological tests and compared reactivity of patients' sera to IFA, immunoblot and ELISAs using whole-cells of spirochetes. We also began large-scale genomic sequencing projects with Borrelia hermsii and Borrelia turicatae. Comparisons of these genomes to Borrelia burgdorferi will elucidate genetic differences that underlie unique biological properties of each organism. Genomic sequences will also allow us to use microarray analysis of spirochetes in ticks versus mammals.